1. Field of Invention
The invention relates to an electrophotographic image forming apparatus, such as a laser printer.
2. Description of Related Art
Eelectrophotographic image forming apparatus are well known in the art. These devices, such as a laser printer, typically includes a photosensitive drum, a charger, a laser scanner, a developing roller, and a transfer roller. After the surface of the photosensitive drum is uniformly charged by the charger, the surface of the photosensitive drum is irradiated with a laser beam emitted from the laser scanner, and an electrostatic latent image is formed based on predetermined image data.
Toner carried on the developing roller is supplied to the electrostatic latent image formed on the surface of the photosensitive drum. The toner deposited on the surface of the photosensitive drum is transferred to a sheet passing between the photosensitive drum and the transfer roller.
Although most of the toner deposited on the photosensitive drum is transferred to the sheet, part of the toner remains on the photosensitive drum. The remaining toner is collected by the developing roller and recycled.
However, when a large amount of toner remains on the photosensitive drum and is not thoroughly collected by the developing roller, the remaining toner adversely affects the next image to be formed on the photosensitive drum, causing a deterioration in print quality.
The invention provides an image forming apparatus that is simply structured at a low cost and can reliably remove developing agent remaining on an image bearing member.
According to one exemplary aspect of the invention described herein, a bias is applied to a cleaning member so that the cleaning member is kept at a fixed potential, and a potential of an image bearing member that contacts the cleaning member is selectively changed between a first potential and a second potential. The bias applied to the cleaning member is higher than the first potential and lower than the second potential.
When the image bearing member is at the first potential, developing agent remaining on the image bearing member is collected by the cleaning member due to a potential difference between the image bearing member and the cleaning member.
When the image bearing member is at the second potential, the developing agent collected by the cleaning member returns to the image bearing member due to a potential difference between the image bearing member and the cleaning member.
In order to change the potential of the image bearing member between the first potential and the second potential, a bias applied to a transfer member is switched between a first transfer bias and a second transfer bias. When the first transfer bias is applied to the transfer member, the image bearing member bears the first potential. When the second transfer bias is applied to the transfer member, the image bearing member bears the second potential. A selector switch is provided to switch between a first transfer power source for outputting the first transfer bias and a second transfer power source for outputting the second transfer bias.
By changing the potential of the image bearing member, which is accomplished by a simple low-cost structure, cleaning of the transfer member and cleaning of the cleaning member can be performed concurrently.